1. Field of the Invention
The present invention relates to a gas adsorbing canister.
2. Description of the Related Art
A known gas adsorbing canister includes a casing having a casing body, formed into a bottomed tubular shape with an end wall at one end thereof, and a lid member for closing the other end of the casing. A partition wall extends toward the lid member. One end of the partition wall is connected to the end wall. Opposite sides of the partition wall are connected to an inner surface of the casing body. First and second filters are fixedly disposed within the casing body on opposite surfaces of the partition wall. First and second chambers are defined between the first and second filters and the end wall, respectively. A third filter is superposed and carried on an inner surface of a support plate which is fitted to the other end of the casing body. The support plate has a large number of communication bores which permit a gas to flow therethrough. The third filter is disposed at a distance from the other end of the partition wall. First and second adsorbent layers are formed by adsorbents. The first and second adsorbent layers are retained between the first and second filters and the third filter, respectively. A spring is accommodated within a third chamber. The third chamber is defined between the support plate and the lid member. The spring biases the support plate in a direction to compress the first and second adsorbent layers.
Such a canister is conventionally constructed as shown in FIG. 12. Specifically, the first and second adsorbent layers 29 and 30 are resiliently retained between the first and second filters 24 and 25 and the third filter 28 by a spring force of the spring 32. Therefore, when the adsorbent, such as activated carbon, is finely pulverized by vibration or the like, the generation of a vacant space, due to a reduction in volume of each of the adsorbent layers 29 and 30, can be prevented, thereby avoiding a reduction in adsorbing efficiency of the canister.
In the above conventional structure, however, because of different cross-sectional areas of the first and second adsorbent layers 29 and 30, the support plate 27 and the third filter 28 may be inclined from a normal state, shown by a dashed line, toward the adsorbent layer of the larger cross-sectional area, i.e., toward the first adsorbent layer 29 at a fulcrum provided at a point corresponding to the other end of the partition wall 19. If such an inclination tendency is increased, a gap is created between the support plate 27, the third filter 28 and the inner surface of the casing body 17. The adsorbent is dropped through the gap into the third chamber 31. Such a phenomenon is liable to be produced by the expansion of the casing body resulting from the pressurization of the inside of the casing body 17. The production of such a phenomenon brings about a reduction in adsorbing efficiency of the canister.
There is a conventionally known canister of a construction in which a plurality of springs are accommodated and disposed in the third chamber 31, so that spring forces are equally applied to adsorbent layers 29 and 30. Even in such a construction, the inclination of the third filter 28 and the support plate 27 cannot be prevented.